Population aspects of human working capacity.

Population measurements of human physical working capacity are reviewed. Problems of technique include an appropriate sample size, allowance of sampling bias, selection of an appropriate criterion of working capacity, and standardization of test methodology. The impact of constitution has been studied in terms of overall variance of data, frequencies of genetic markers, and twin sibling studies. Environmental experiments have compared similar races in different environments and vice versa. Athletes have been examined as examples of a combined genotypic and phenotypic response. Adaptations to the environment include adverse climate (extremes of heat, cold, rain and drought), hilly terrain and extreme high altitudes; an enhanced working capacity in hilly districts and circumpolar regions probably reflects vigorous daily activity. Socio-economic determinants of working capacity include nutrition, family size, chronic disease, and daily activity. Population differences in the course of growth and ageing seem to reflect differences of nutrition and daily activity. Population scientists have yet to define clearly the relative importance of phenotypic and genotypic adaptation in the development of working capacity; however, studies arising from the International Biological Programme have made valuable contributions to both test methodology and the understanding of interactions between man and his environment.